FIG. 1 is a perspective view illustrating a reactor vessel in a nuclear power plant in the related art.
In general, a primary-side main facility of a westinghouse type nuclear power plant includes a reactor vessel 100, and a total of six nozzles 110 of three inlet nozzles and three outlet nozzles on an outer periphery of the top of the reactor vessel 100.
Further, the six nozzles 110 mounted on the reactor vessel 100 and a pipe 130 are connected with each other by a dissimilar metal weld part 120.
Herein, the reactor vessel 100, the pressurizer, the steam generator, the coolant pump, and the like are made of low carbon steel and a main pipe is made of stainless steel.
Further, the dissimilar metal weld parts 120 connecting the nozzle 110 and the pipe 130 are welded to each other by an alloy 82/182 material that can buffer different mechanical properties of materials.
However, according to an apparatus having a configuration in the related art, with an increase in operating years of the nuclear power plant, primary water stress corrosion cracking in the dissimilar metal weld parts 120 gradually increases.
Since an operator needs to approach an inner part of the reactor vessel to replace each of machining, examination, and welding devices which are independently configured according to a required process in order to remove the aforementioned defect, there was a problem in that an error may occur in an operating position according to the device.
Since a safety of the operator is significantly influenced by the vicinity of a nozzle part of the reactor vessel as a zone which is polluted by radioactivity, there was a problem in that it is difficult to perform repairing by hand.